In a dynamic type speaker, a voice coil bobbin having a voice coil wound therearound is basically fixed at an inner circumferential edge of a cone diaphragm whereas a peripheral edge of the diaphragm is secured to a frame via an edge portion. Moreover, a circumferential edge of a damper is fixed to the voice coil bobbin whereas a peripheral edge of the damper is secured to the frame. That is to say, the edge portion or the damper constitutes a suspension in a vibration system such as the diaphragm or the voice coil.
A deep bass reproducing speaker which is called a woofer or a sub woofer for use in, for example, a vehicle-mounted audio system is configured such that a satisfactory sound pressure level in a bass region can be ensured by taking a great amplitude stroke of the diaphragm since there is a limitation on a diameter of a diaphragm.
The damper, in particular, constituting the above-described suspension in the vibration system need be equipped with a function for ensuring an amplitude stroke equal to that at the edge portion without any contact of the voice coil with a pole piece or a yoke constituting a magnetic gap.
As a consequence, it is difficult to give great compliance to the damper. There arises a problem of degradation of power linearity caused by the occurrence of non-linearity of a movable load in the damper in the speaker in which the great amplitude stroke is ensured. In addition, there is carried a problem that a mechanical fatigue of the damper occurs earlier than that of the edge portion.
In the meantime, a corrugation damper having a bellows shape in a cross section is frequently used as the damper in order to ensure the compliance. However, there arises a problem that peculiar vibrations or scratchy noises occur due to deformation between adjacent bellows accompanied with an amplitude motion. This prominently occurs in the speaker having the great amplitude stroke of the diaphragm, as described above.
In view of this, the Applicant has already filed the application of a speaker device in which, for example, a rolled edge having a function similar to that of the above-described edge portion is adopted in place of the above-described damper, and further, the rigidity of the diaphragm in the vibration direction can be enhanced, as disclosed in the gazette of Patent Document 1.
With a configuration of the speaker disclosed in Patent Document 1, it is possible to solve the problems experienced by the use of the above-described damper, and further, to enhance the rigidity of the diaphragm in the vibration direction, thus achieving excellent acoustic characteristics as a bass reproducing speaker.
Patent Document 1: Japanese Patent Application Laid-open No. 2005-191746